Consumers have started to acquire high definition televisions, often referred to as “HDTV”. One type of HDTV is the rear projection television system, or “RPTV”. Traditional RPTVs use either cathode ray tubes that project picture data onto the rear of a transmission screen or microdisplay technologies that form images through the use of solid state “imagers” in conjunction with a light engine that in turn project images onto the rear of the transmission screen. The term “imager” is often used in the trade as formal nomenclature for the term “microdisplay.”
One type of microdisplay imagers are reflective liquid-crystal-on-silicon devices, known as “LCoS”. For LCoS imagers to be useful in display systems, a projection engine optical architecture having high performance and low cost is necessary. A ‘projection engine’ or “light engine” generally refers to the components of a display from lamp to the projection lens. The various embodiments disclosed herein teach disclose a projection engine architecture capable of high performance and low cost, both of which are requirements in the competitive display market.
All projection engine architectures must perform the following functions. The engine must collect, condense and condition raw bulb light emission for illumination of the imager devices. Then, the engine must separate the white light from the lamp into three primary colors (red, green and blue), polarize each color appropriately for presentation to the LCoS imagers. The engine must then analyze polarization of the modulated primary images after reflection from the LCoS imagers, and then combine the primary colors through a projection lens that focuses the combined image onto the screen.
A primary property of LCoS imagers is polarization of light. The degree to which polarization is processed and transformed within the projection engine is of paramount importance to its total image performance. Polarization is commonly resolved into two opposite spatial components, “P” and “S”. A vector quantity pertinent to this polarization property is the “polarization state” of a particular beam of light. The polarization states of interest are “P-polarization”, which is the alignment of the polarization vector with the electric field vector of the light waves, and “S-polarization”, which is the polarization vector perpendicular to the electric field vector of the light waves. As used herein, polarization logic means that a polarization vector pointing in any direction of the compass about the optical axis can be resolved into its two constituent components in the S direction or the P direction. The quality of the contrast in the engine polarization states is directly converted into luminance contrast in the image, which the viewer sees as the full black and full white states of the image. Thus, high contrast between P-polarization and S-polarization is necessary for high image quality.
There continues to be a need for a low cost, high performance, optical engine for use in rear projection displays having improved performance and lower cost than those of the prior art.